The objective of these experiments is to determine the signals that control the intracellular trafficking of kainate receptors. Kainate receptors (KARs) comprise a family of ionotropic glutamate receptors whose role in brain physiology and pathology is poorly understood. Little is known regarding the signals that regulate the assembly, transport, and membrane expression of KARs. Physiological characterization of recombinant KARs demonstrated that "low-affinity" subunits, encoded by the GIuR5, GluR6 and GluR7 genes, formed functional glutamate receptors. In contrast, the "high-affinity" subunits KA-1 and KA-2 did not form functional homomeric ion channels, but rather modified the physiological properties of the channel-forming subunits. What is the basis for this difference in functionality between low- and high-affinity KAR subunits? Recent results provide some clues and form the foundation for this project application. Recent results provide some clues and form the foundation for this project application. While characterizing a newly generated anti-KA-1 antibody we found that much, if not all, of KA-1 subunit protein expressed in mammalian cells is retained in the endoplasmic reticulum (ER) and does not reach the cell surface as a homomeric receptor. This pattern of ER retention suggested the possibility that KA-1 and KA2 subunits may either contain ER retention signals or lack ER export motifs in their protein sequence. Strikingly, an examination of the carboxy-terminal sequences revealed that only three kainate receptor subunits contained RXR sequences-KA-1, KA-2 and the weakly expressed GluR7b receptor. The correlation between lack of function and presence of RXR sequence make these motifs likely candidates for KAR ER retention signals. In this project application we will examine the role of RXR motifs in determining the trafficking of KARs. First, using a combination of immunohistochemical and physiological techniques we will test the hypothesis that RXR motifs in the carboxyterminal domains of the KAR subunits act as endoplasmic reticulum retention signals. Second, we will determine if GIuR5 and GluR6 subunits contain carboxy-terminal signals that act as masking domains for retention motifs on KA-1 and KA-2 subunits. Third, a potential role phosphorylation in modulation of trafficking will be examined. These experiments are important for understanding what cellular mechanisms control the subunit composition of KARs and how functional expression of aberrant receptor complexes may alter excitatory neurotransmission.